1. Field of the Invention
The present invention relates to fiber-optic data communication.
2. Description of the Related Art
Multi-mode optical communication standards, such as the 100G-SR4 standard of IEEE 802.3, rely upon direct-modulated laser sources that are integrated within the transceiver module. For example, FIG. 1A shows a transceiver module 101 having a direct-modulated laser 103 integrated therein. The direct-modulated laser 103 is turned on and off to produce an on-off keyed light transmission at an output 104. The transceiver module 101 also includes a receiver module 105 configured to receive an encoded light transmission at an input 106 for decoding. It should be understood that the direct-modulated laser 103 is implemented directly and physically within the transceiver module 101.
Single-mode optical communication typically uses an indirect modulation scheme (though direct modulation is also possible) in which continuous wave light generated by a laser is modulated by a modulator. For example, FIG. 1B shows a transceiver module 107 having an indirect-modulated laser configuration in which a laser light source 109 within the transceiver module 107 produces continuous wave light that is modulated by an independent modulator 111 within the transceiver module 107 to generate a light stream of encoded data for transmission at an output 112 of the transceiver module 107. The transceiver module also includes a receiver module 113 configured to receive an encoded light transmission at an input 114 for decoding. It should be understood that the laser light source 109 is implemented directly and physically within the transceiver module 107.
In some configurations, a laser light source is shared across multiple transceivers within the same transceiver module, where transmitters of the multiple transceivers transmit at the same wavelength of light, such as in accordance with optical communication specification 100G-PSM4 of the parallel single mode 4-lane multi-source agreement (PSM4 MSA) group. For example, FIG. 1C shows a laser light source 117 connected to provide laser light to multiple transceivers within a transceiver module 115. The multiple transceivers are defined by multiple modulators 119-1 to 119-N and multiple receiver modules 121-1 to 121-N. The multiple modulators 119-1 to 119-N are parts of respective transmitter modules configured to generate multiple light streams of encoded data for transmission at respective outputs 120-1 to 120-N of the transceiver module 115. The laser light source 117 supplies continuous wave light to the multiple independent modulators 119-1 to 119-N within the same transceiver module 115 as the laser light source 117. The multiple receiver modules 121-1 to 121-N are configured to receive encoded light transmissions at respective inputs 122-1 to 122-N for decoding. It should be understood that the laser light source 117 is implemented directly and physically within the transceiver module 115.
Wavelength division multiplexing (WDM) has been proposed to scale bandwidth per optical fiber in fiber-optic data communication systems, such as in accordance with optical communication standard 100G-LR4 of IEEE 802.3). FIG. 1D shows a transceiver module 123 for WDM optical data communication in which multiple laser light sources 125-1 to 125-N are implemented to respectively supply continuous wave light of different wavelengths to multiple modulators 127-1 to 127-N of corresponding multiple transmitters. Each of the multiple modulators 127-1 to 127-N is configured to generate a respective light stream of encoded data based on the wavelength of the continuous wave light that it receives from its corresponding laser light source 125-1 to 125-N. The multiple light streams of encoded data output by the multiple modulators 127-1 to 127-N are multiplexed onto a single optical fiber in accordance with the WDM optical data communication standard by a wavelength multiplexer 129 for transmission at an output 130 of the transceiver module 123. The multiple transmitters within the transceiver module 123 also include multiple receiver modules 131-1 to 131-N configured to receive encoded light transmissions for decoding from a wavelength demultiplexer 133. The wavelength demultiplexer 133 is configured to receive a transmission of multiple light streams of encoded data that have been multiplexed onto a single optical fiber in accordance with the WDM optical data communication standard at an input 134, and supply separate ones of the multiple light streams of encoded data to corresponding ones of the multiple receiver modules 131-1 to 131-N for decoding. It should be understood that the multiple laser light sources 125-1 to 125-N are implemented directly and physically within the transceiver module 123.
The laser light sources used for WDM optical data communication require precise temperature control due to wavelength drift of the laser light sources with variation in temperature and due to the close spacing of the optical wavelength channels as defined by the WDM optical communication standard. Such precise temperature control can be costly, bulky, and power-consuming. Therefore, WDM optical data communication using multiple laser light sources with precise temperature control can be undesirable for shorter reach communication networks such as the networks present in data centers. Coarse wavelength division multiplexing (CWDM) optical data communication, such as in accordance with optical communication specification 100G-CWDM4 of the coarse wavelength division multiplexing 4-lane multi-source agreement (CWDM4 MSA) group, relaxes the wavelength channel spacing requirements in order to simplify the thermal control of the multiple laser light sources.
Both WDM and CDWM use multiple laser light sources that are directly and physically implemented within the transceiver module to generate the set of wavelengths that are needed for the optical data communication. And, typical laser light sources implemented within the transceiver module are configured to output only 5 milliWatts (mW) to 10 mW of power. However, there are several drawbacks to having the laser light sources implemented directly and physically within the transceiver module. For example, one such drawback is difficulty of replacement of the laser light source. Within the optical data communication system, the laser light source is the component that has the shortest mean time to failure. Replacement of a malfunctioning/failed laser light source requires replacement of the entire transceiver module, which is logistically difficult and costly.
Another drawback of having the laser light source implemented directly and physically within the transceiver is that the laser light source, which is a thermally-sensitive component, is exposed to and must tolerate the same range of temperature variation as the other transceiver components. This exacerbates the aforementioned issue regarding precise temperature control of the laser light sources due to wavelength drift caused by variation in temperature. Additionally, when the laser light source is implemented directly and physically within the transceiver, the laser light source is confined within the small form factor of the transceiver which makes thermal dissipation more difficult, thereby lowering the efficiency and reliability of the laser light source.
Another drawback of having the laser light source implemented directly and physically within the transceiver is that the laser light source is operated at relatively low power (enough to power a single link), which can adversely affect wall-plug efficiency. Also, there are form factor and material constraints associated with integration of the laser light source within the transceiver module. Another drawback of having the laser light source implemented directly and physically within the transceiver is that the power budget of the laser light source adds to the power budget of the transceiver module, which compounds the power dissipation problem faced by small form factor transceiver modules.
Also, as disclosed in U.S. Pat. No. 7,715,714, use of a centralized laser power grid having an array of single-wavelength continuous wave laser light sources in a packet-switched optical network has been considered. However, such methods that implement the centralized laser power grid use wavelength-addressable switches to steer continuous wave laser power to specific optical links, which results in an architecture that is significantly different than that of the inventive embodiments disclosed herein with regard to the present invention. It is within this context that the present invention arises.